This invention relates to air diffusers wherein an air impeller, such as a fan, discharges air through a housing, airflow control apparatus, or the like associated with the fan. The discharge can be either into a confined space such as a room or into the atmosphere.
This invention will be discussed in connection with a building rooftop ventilator which uses a centrifugal fan to draw air from a building interior and discharges that air into the ambient atmosphere. It is to be appreciated, that the invention is not necessarily limited to that type of application.
Generally, such rooftop units are mounted on a curb which is attached to the roof and communicates with the building air delivery system. Specifically, the unit exhausts air from the building to the atmosphere. The centrifugal fan used as the air impeller and its associated drive elements are covered by a shroud, or other type of housing, for protection against the weather. An air discharge opening is provided in the protective housing. Exhaust air from the building travels through the interior of protective housing and out the discharge opening to the atmosphere.
In the past, such building air exhaust systems have been, for the most part, what may be referred to as a bulk transfer of air. That is, they have merely provided a forced withdrawal of air from the building interior and a more or less random discharge through the protective structure with little, if any, thought being given to aerodynamic properties. The problems and/or shortcomings of such prior systems have been relatively ineffective and inefficient transfer of air from the building interior to the atmosphere, and noise generation. Ineffective and inefficient air transfer impacts in a negative manner on the building air exhaust system. This, in turn, can impact negatively on the overall building air delivery system. It can also create a noise problem, of particular concern where the building is in a heavily populated urban area; although even in an isolated building noise can be a problem with respect to the building occupants and any operations carried on in the building.
It has been noted in such prior systems that part of the kinetic energy imparted to the exhaust air by the air impeller, and which could best be utilized in enhancing exhaust airflow, has been lost due to the random uncontrolled airflow within the rooftop unit.